Java 关于LinkedBlockingQueue源代码的一些混淆

在LinkedBlockingQueue的源中

public void put(E e) throws InterruptedException {
    if (e == null) throw new NullPointerException();
    // Note: convention in all put/take/etc is to preset local var
    // holding count negative to indicate failure unless set.
    int c = -1;
    Node<E> node = new Node<E>(e);
    final ReentrantLock putLock = this.putLock;
    final AtomicInteger count = this.count;
    putLock.lockInterruptibly();
    try {
        /*
         * Note that count is used in wait guard even though it is
         * not protected by lock. This works because count can
         * only decrease at this point (all other puts are shut
         * out by lock), and we (or some other waiting put) are
         * signalled if it ever changes from capacity. Similarly
         * for all other uses of count in other wait guards.
         */
        while (count.get() == capacity) {
            notFull.await();
        }
        enqueue(node);
        c = count.getAndIncrement();
        // #Question 1
        if (c + 1 < capacity)
            notFull.signal();
    } finally {
        putLock.unlock();
    }
    if (c == 0)
        signalNotEmpty();
}

1） 如果队列已满，则条件为

true

。如果我理解正确，

notFull.signal（）

调用在

LinkedBlockingQueue

的当前实现中实际上是不必要的。因为所有锁和条件都是私有的，所以派生类也不会从调用中受益。所以我想这只是为了确保将来对类的扩展的正确性

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2） 获取

takeLock

是必要的，以防止其他线程在发出

notEmpty

信号时清空队列。

thx…因此我们在jdk源代码中发现了一些额外的代码，我很难相信这一点。你是对的。我希望我没有忽略什么。

 private void signalNotEmpty() {
            final ReentrantLock takeLock = this.takeLock;
            takeLock.lock();
            try {
                notEmpty.signal();
            } finally {
                takeLock.unlock();
            }
        }